For the injection of fuel into internal combustion engines, use is made inter alia of direct fuel injection. For this purpose, use is made of piezo injectors, the nozzle needle of which is driven by way of a piezo actuator. Here, virtually clearance-free coupling between the piezo actuator and nozzle needle is necessary, though this is difficult to maintain owing to thermal changes in length in the piezo injector. To eliminate this problem, the nozzle needle is coupled hydraulically to the piezo actuator. For this purpose, the piezo injector has an actuator chamber in which the piezo actuator is arranged. A control piston is arranged in a control piston bore. The control piston has a first face side facing toward the piezo actuator. A section of the control piston bore delimited by the first face side forms a first control chamber. A section of the control piston bore situated opposite the first control chamber forms a spring chamber. The control piston is arranged between the first control chamber and the spring chamber. A nozzle needle has a second face side. The nozzle needle guides a nozzle needle sleeve, wherein the nozzle needle sleeve and the second face side delimit a second control chamber. Furthermore, a connecting bore is provided between the first control chamber and the second control chamber. A leakage pin, which is arranged between the piezo actuator and the first face side and in a leakage pin bore, effects coupling of the piezo actuator and of the control piston. If the piezo actuator is actuated, the leakage pin presses against the control piston and displaces the latter in the direction of the nozzle needle.
Owing to the pressure difference between the control chamber and the spring chamber, a fluid flow takes place laterally through a gap between the control piston and the control piston plate. Here, the fluid flow is dependent on the gap width and the temperature of the fuel. Owing to the great temperature differences during the operation of the injector with cold and hot fuels and with a cold and hot internal combustion engine, the fluid flow changes in a manner dependent on the temperature of the injector and of the fuel. This can lead to changed operating characteristics.